Such an aspiration instrument is known in practice and is described in a brochure obtainable from Cooper Companies Inc., established at One Bridge Plaza, Fort Lee, N.J. 07024, USA. The known aspiration instrument is designed for the collection of cell material from subcutaneous tissue for purposes of cytological research. The known aspiration instrument is made ready for use by fastening a hypodermic needle to the cylinder and subsequently depressing the plunger against the force of the pre-compression means until the plunger is locked in the second position. During this process pre-compression means are pre-compressed. The piston is now situated at the distal end of the cylinder. The hypodermic needle can then be introduced into the tissue to be examined, following which the locking can be undone simply by a finger movement. Under the influence of the compressed pre-compression means, the plunger--and thus the piston--moves back to the first position, while a partial vacuum is created in the cylinder, as a result of which cell tissue is aspirated. When sufficient cell tissue has been collected, the partial vacuum in the front part can be neutralized by deforming the piston by means of a pawl and consequently admitting air to the cylinder.
In the case of the known aspiration instrument the partial vacuum is created beforehand, so that the person performing the biopsy, called the doctor below, can then concentrate fully on the collection of the cell material. The known aspiration instrument in this case can be operated with one hand, with the result that the collection of the cell material can be accurate and the doctor can advantageously use the other hand for, for example, fixing the tissue to be examined during the operation. Moreover, the working distance from the hand to the tissue to be punctured is short, with the result that the operation can be performed with a high degree of accuracy.
However, the known aspiration instrument is designed for a single use. In practice, this means that the aspiration instrument has been found too expensive for human applications, and certainly for veterinary applications. Due to the relatively high wastage of material involved in single use, the known aspiration instrument is also environmentally unfriendly. Besides, in various countries there are different procedures for the collection of cell material, which in practice can mean that it is compulsory to collect cell material twice from one patient. This even further emphasizes the abovementioned drawbacks of the known aspiration instrument.
The object of the present invention is to provide an aspiration instrument of the type mentioned at the beginning which does not have the above mentioned disadvantages, while at the same time the above mentioned advantages are retained.